In applicant's U.S. Pat. No. 3,908,496, entitled "Hydraulic Shearing Machine", granted Sept. 30, 1975, a shearing machine is disclosed wherein the bar being sheared is engaged on both sides of the shear plane by a balanced back support and hold-down clamping system. The balanced clamping system minimizes distortion and bending of the bar during shear. Such shearing machine is capable of shearing with desirable results many metals including many alloys theretofore considered unshearable. Even so, there are other metals that heretofore could not be sheared effectively by such a shearing machine due to the formation of stress cracks and the like, nor, to applicant's knowledge, could they be sheared effectively by any other commercially available shearing machine. These metals include, for example, high temperature alloys used in the aircraft industry, titanium, 52100 steel in an as-rolled condition, and other metals. Accordingly, other methods had to be employed for cutting them. One known method is to use hack saws or band saws to cut the metal bars into pieces while other methods involve the use of milling cutters, abrasive cutters or torch cutters to cut the bars. These methods, however, are all very costly and slow.
For some high alloy steels such as 4340 steel, it is also known to heat the metal bar to a high temperature and then to shear it while it is still hot to eliminate cracking. Typically, the entire bar is heated in a gas furnace to a relatively high temperature depending on the alloy. For example, a 4340 steel bar might be heated to 900.degree. to 1000.degree. F. This heating of the bar, however, is costly and time consuming. For instance, it typically takes several minutes and substantial amounts of energy to heat a bar of say 5-inch bar size to such high temperature.
It is also known to heat the metal bar by employing resistance heating or induction heating techniques. Here again, the heating of the bar is extremely costly. Moreover, a tremendously large power unit is needed to heat the larger diameter bars to the required temperatures at which they can be sheared.
A single induction heating coil has previously been used to heat small diameter bars of uranium to a relatively high temperature such as 600.degree. in a relatively small area or zone where the bar is to be sheared. When the bar reaches the required temperature as determined by an optical pyrometer, it is immediately fed into the shear and sheared. While the optical pyrometer might be used effectively in a controlled environment, a forge shop is normally not a good environment for the optical pyrometer. In the forge shop, the pyrometer is likely to get dirty, or be knocked or vibrated out of adjustment or knocked off or damaged in some way. Also, the optical pyrometer only measures surface temperature of the bar, which will be reached much sooner than the desired core temperature for producing the desired quality of cut by hot shearing, particularly when larger diameter bar stock is being sheared.